1. Field
The present disclosure relates to an automatic transmission controller.
2. Description of the Related Art
To improve driving performance and drivability, the number of gear ratios of an automatic transmission for an automobile is being increased. In general, an automatic transmission includes engagement mechanisms, such as planetary gear mechanisms, clutches, and brakes. The gear ratio of the automatic transmission is changed by changing the power transmission path by using the engagement mechanisms. Such an automatic transmission includes a torque converter (starting mechanism) that is disposed between a drive source and a driving wheel of a vehicle and that transmits rotational power from the drive source to the driving wheel.
In recent years, automatic transmission controllers that perform so-called “idling neutral control” when a vehicle stops have been increasingly used. The term “idling neutral control” (hereinafter referred to as “idling N control”) refers to control in which the automatic transmission is automatically changed to an idle neutral mode in order to reduce energy loss in the torque converter when the vehicle stops.
When a vehicle that performs idling N control stops on, for example, an uphill slope, it is not possible to prevent backward movement of the vehicle on the slope because the torque converter does not have a creep torque or has only a very small creep torque.
For example, Japanese Patent No. 4711443 describes an automatic transmission controller that detects the inclination angle of a slope with high precision by using a rotation sensor for detecting a backward slope in order to prevent backward movement of the vehicle when control of the vehicle is returned from idling N control. The rotation sensor, which actively detects backward movement, has a special structure because it is difficult for an ordinary sensor to detect backward movement of a vehicle because the rotational speed of a wheel of the vehicle is low when the vehicle moves backward.
Japanese Patent No. 4839865 describes an automatic transmission controller that detects the inclination angle at a position at which a brake of a vehicle is operated by detecting the master cylinder pressure of the brake. The automatic transmission controller includes a brake hydraulic pressure sensor for detecting the amount by which a brake pedal is depressed. If the brake hydraulic pressure detection sensor detects a hydraulic pressure that is greater than or equal to a predetermined value A, a brake-pedal-depression condition is satisfied and a creeping-prevention control (neutral control) is performed. There is a difference between the threshold of the amount by which the brake pedal is depressed for starting neutral control and the threshold for returning from neutral control, that is, there is so-called hysteresis between the conditions for starting and returning from the control. Therefore, starting of neutral control when the driver does not intend to can be prevented. Moreover, because neutral control is not started unless the brake pedal is depressed by a considerable amount, the automatic transmission controller has an advantage in that a vehicle can be driven very easily when parallel-parking or garaging the vehicle, for which it is necessary to drive the vehicle at a creeping speed or less.